I know there have been plenty of discussions (understatement of the century?) about the proportion of power put in at the cranks of various types of 'bent that is lost to frame flex, idlers, drivetrain inefficiency of whatever kind.

This can be measured by using two power meters - one at the input side (the crank) and one at the output (the wheel). For example:

- it would be possible to put 250W into the cranks of a Bacchetta stick bike and a swoopy Euro-style bike and see which one has more watts hitting the road.
- it would be possible to swap an OEM idler for a Terracycle one, a bigger or a smaller one, and see if there was any effect
- we could pry apart drivetrain efficiency and frame flex by bracing the bike in a stand (eliminating flex) and comparing with the bike freely-pedalled
- if I can find a Cruzbike anywhere we could compare MBB and RWD efficiency

Unfortunately I already own a PowerTap, but not a crank-based power meter. And much as I'd love to be able to justify it, I simply can't get one past the CFO just to measure frame flex and drivetrain efficiency. I've tried to find one to borrow but it doesn't seem like it's going to happen.

However, a comment on my most recent article on recumbent efficiency has me wondering if there might be enough collective interest to "crowd source" a crank-based (or pedal-based) meter for these purposes.

That is, people donate a proportion of the cost of a power meter (I'd obviously be contributing too) in exchange for the results of testing, and input into what is tested.

As I don't want to end up enriching myself, I was thinking that after testing the bikes / trikes I can get hold of locally / through Laid-Back-Bikes the power meter could be:

- raffled off and given to one of the donors (the more donated, the more tickets you get, and we could draw by video )
- directly donated to a relevant cause who can put it to good use (BROL?)
- sold and the money donated to a good cause (some type of bike-related charity?)

Crank meters aren't cheap, but on the other hand they aren't crazy expensive if split between a group: a Power2Max would come in under 1200USD from a quick look at their site.

To do the comparison, you will need to time-sync the results of the two meters somehow. Any ideas about how to make that work? Will a Garmin allow you to record the results of two power sensors simultaneously?

Into the northern region of Canada, at the close of the nineteenth century, rode Dudley Do-Right of the Mounties, lonely defender of justice and fair play: handsome, brave, daring... and hopelessly lost.

SC - Judging by how poorly received past suggestions have been for folks to conduct field tests using power meters to determine parameters such as CdA and Crr instead of merely speculating all the time or citing race results, I'd say you've got an uphill battle ahead of you.

To do the comparison, you will need to time-sync the results of the two meters somehow. Any ideas about how to make that work? Will a Garmin allow you to record the results of two power sensors simultaneously?

If you really want to know (because you are actually going to do it), email or PM RChung. He's done this stuff. (not on 'bents, though).

If you really want to know (because you are actually going to do it), email or PM RChung. He's done this stuff. (not on 'bents, though).

Well, I'm extremely unlikley to actually do this. My style of riding is such that there would be very little benefit from knowing. But I am certainly curious about how this could be accomplished. I can fully appreciate the desires of more speed oriented cyclists to know how effectively their machines transmit the power.

Into the northern region of Canada, at the close of the nineteenth century, rode Dudley Do-Right of the Mounties, lonely defender of justice and fair play: handsome, brave, daring... and hopelessly lost.

I always wonder about those losses, too. However, the more I read about power meters the more confused I become. From what I can tell, even if power meters are calibrated they operate within a margin of error (about 2%, I believe), so that even when they’re used in the same session they can give different power readings. You’ve probably read the reviews on the dcrainmaker website, and you probably understand the numbers a lot better than I can (I just gloss over them) but he’s done a lot of comparison tests. He has a data logger which can capture the output from multiple ANT+ devices.

I can’t even decide if it’s worth me buying a power meter, and much less deciding on which to buy. However, if I end up with something like the Garmin Vectors I could loan them for you to test. On that note, perhaps someone in the Edinburgh cycle clubs would be willing to do the same.

I always wonder about those losses, too. However, the more I read about power meters the more confused I become. From what I can tell, even if power meters are calibrated they operate within a margin of error (about 2%, I believe), so that even when they’re used in the same session they can give different power readings. You’ve probably read the reviews on the dcrainmaker website, and you probably understand the numbers a lot better than I can (I just gloss over them) but he’s done a lot of comparison tests. He has a data logger which can capture the output from multiple ANT+ devices.

I can’t even decide if it’s worth me buying a power meter, and much less deciding on which to buy. However, if I end up with something like the Garmin Vectors I could loan them for you to test. On that note, perhaps someone in the Edinburgh cycle clubs would be willing to do the same.

The point of a power meter isn't the hard number.
It's tracking your personal improvement.
For that 2% is plenty good enough.

The testing described in this thread would have to be done with enough runs to manage the variations.

I know for training a power meter just has to be consistent rather than absolutely accurate, but for measuring drivetrain losses wouldn’t any differences between the two devices make the test results questionable? Drivetrain losses of 1 – 2% are frequently quoted, and that’s less than the potential variation between the two power meters.